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Use generics for DepSets

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Use Go's generics for DepSets so they don't require a type-specific
wrapper and reflection.

Test: depsets_test.go
Change-Id: I22ba0b7d680d37d2cd05230b0f560d166c4dd20b
This commit is contained in:
Colin Cross
2022-04-21 12:50:51 -07:00
parent abcfc77717
commit c85750bfe3
26 changed files with 262 additions and 627 deletions
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305
android/depset_generic.go
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@@ -16,10 +16,9 @@ package android
import (
"fmt"
"reflect"
)
// depSet is designed to be conceptually compatible with Bazel's depsets:
// DepSet is designed to be conceptually compatible with Bazel's depsets:
// https://docs.bazel.build/versions/master/skylark/depsets.html
type DepSetOrder int
@@ -43,142 +42,114 @@ func (o DepSetOrder) String() string {
}
}
// A depSet efficiently stores a slice of an arbitrary type from transitive dependencies without
// copying. It is stored as a DAG of depSet nodes, each of which has some direct contents and a list
// of dependency depSet nodes.
type depSettableType comparable
// A DepSet efficiently stores a slice of an arbitrary type from transitive dependencies without
// copying. It is stored as a DAG of DepSet nodes, each of which has some direct contents and a list
// of dependency DepSet nodes.
//
// A depSet has an order that will be used to walk the DAG when ToList() is called. The order
// A DepSet has an order that will be used to walk the DAG when ToList() is called. The order
// can be POSTORDER, PREORDER, or TOPOLOGICAL. POSTORDER and PREORDER orders return a postordered
// or preordered left to right flattened list. TOPOLOGICAL returns a list that guarantees that
// elements of children are listed after all of their parents (unless there are duplicate direct
// elements in the depSet or any of its transitive dependencies, in which case the ordering of the
// elements in the DepSet or any of its transitive dependencies, in which case the ordering of the
// duplicated element is not guaranteed).
//
// A depSet is created by newDepSet or newDepSetBuilder.Build from the slice for direct contents
// and the *depSets of dependencies. A depSet is immutable once created.
//
// This object uses reflection to remain agnostic to the type it contains. It should be replaced
// with generics once those exist in Go. Callers should generally use a thin wrapper around depSet
// that provides type-safe methods like DepSet for Paths.
type depSet struct {
// A DepSet is created by NewDepSet or NewDepSetBuilder.Build from the slice for direct contents
// and the *DepSets of dependencies. A DepSet is immutable once created.
type DepSet[T depSettableType] struct {
preorder bool
reverse bool
order DepSetOrder
direct interface{}
transitive []*depSet
direct []T
transitive []*DepSet[T]
}
type depSetInterface interface {
embeddedDepSet() *depSet
}
func (d *depSet) embeddedDepSet() *depSet {
return d
}
var _ depSetInterface = (*depSet)(nil)
// newDepSet returns an immutable depSet with the given order, direct and transitive contents.
// direct must be a slice, but is not type-safe due to the lack of generics in Go. It can be a
// nil slice, but not a nil interface{}, i.e. []string(nil) but not nil.
func newDepSet(order DepSetOrder, direct interface{}, transitive interface{}) *depSet {
var directCopy interface{}
transitiveDepSet := sliceToDepSets(transitive, order)
if order == TOPOLOGICAL {
directCopy = reverseSlice(direct)
reverseSliceInPlace(transitiveDepSet)
} else {
directCopy = copySlice(direct)
// NewDepSet returns an immutable DepSet with the given order, direct and transitive contents.
func NewDepSet[T depSettableType](order DepSetOrder, direct []T, transitive []*DepSet[T]) *DepSet[T] {
var directCopy []T
var transitiveCopy []*DepSet[T]
for _, t := range transitive {
if t.order != order {
panic(fmt.Errorf("incompatible order, new DepSet is %s but transitive DepSet is %s",
order, t.order))
}
}
return &depSet{
if order == TOPOLOGICAL {
// TOPOLOGICAL is implemented as a postorder traversal followed by reversing the output.
// Pre-reverse the inputs here so their order is maintained in the output.
directCopy = reverseSlice(direct)
transitiveCopy = reverseSlice(transitive)
} else {
directCopy = append([]T(nil), direct...)
transitiveCopy = append([]*DepSet[T](nil), transitive...)
}
return &DepSet[T]{
preorder: order == PREORDER,
reverse: order == TOPOLOGICAL,
order: order,
direct: directCopy,
transitive: transitiveDepSet,
transitive: transitiveCopy,
}
}
// depSetBuilder is used to create an immutable depSet.
type depSetBuilder struct {
// DepSetBuilder is used to create an immutable DepSet.
type DepSetBuilder[T depSettableType] struct {
order DepSetOrder
direct reflect.Value
transitive []*depSet
direct []T
transitive []*DepSet[T]
}
// newDepSetBuilder returns a depSetBuilder to create an immutable depSet with the given order and
// type, represented by a slice of type that will be in the depSet.
func newDepSetBuilder(order DepSetOrder, typ interface{}) *depSetBuilder {
empty := reflect.Zero(reflect.TypeOf(typ))
return &depSetBuilder{
order: order,
direct: empty,
// NewDepSetBuilder returns a DepSetBuilder to create an immutable DepSet with the given order and
// type, represented by a slice of type that will be in the DepSet.
func NewDepSetBuilder[T depSettableType](order DepSetOrder) *DepSetBuilder[T] {
return &DepSetBuilder[T]{
order: order,
}
}
// sliceToDepSets converts a slice of any type that implements depSetInterface (by having a depSet
// embedded in it) into a []*depSet.
func sliceToDepSets(in interface{}, order DepSetOrder) []*depSet {
slice := reflect.ValueOf(in)
length := slice.Len()
out := make([]*depSet, length)
for i := 0; i < length; i++ {
vi := slice.Index(i)
depSetIntf, ok := vi.Interface().(depSetInterface)
if !ok {
panic(fmt.Errorf("element %d is a %s, not a depSetInterface", i, vi.Type()))
}
depSet := depSetIntf.embeddedDepSet()
if depSet.order != order {
panic(fmt.Errorf("incompatible order, new depSet is %s but transitive depSet is %s",
order, depSet.order))
}
out[i] = depSet
}
return out
}
// DirectSlice adds direct contents to the depSet being built by a depSetBuilder. Newly added direct
// contents are to the right of any existing direct contents. The argument must be a slice, but
// is not type-safe due to the lack of generics in Go.
func (b *depSetBuilder) DirectSlice(direct interface{}) *depSetBuilder {
b.direct = reflect.AppendSlice(b.direct, reflect.ValueOf(direct))
// DirectSlice adds direct contents to the DepSet being built by a DepSetBuilder. Newly added direct
// contents are to the right of any existing direct contents.
func (b *DepSetBuilder[T]) DirectSlice(direct []T) *DepSetBuilder[T] {
b.direct = append(b.direct, direct...)
return b
}
// Direct adds direct contents to the depSet being built by a depSetBuilder. Newly added direct
// contents are to the right of any existing direct contents. The argument must be the same type
// as the element of the slice passed to newDepSetBuilder, but is not type-safe due to the lack of
// generics in Go.
func (b *depSetBuilder) Direct(direct interface{}) *depSetBuilder {
b.direct = reflect.Append(b.direct, reflect.ValueOf(direct))
// Direct adds direct contents to the DepSet being built by a DepSetBuilder. Newly added direct
// contents are to the right of any existing direct contents.
func (b *DepSetBuilder[T]) Direct(direct ...T) *DepSetBuilder[T] {
b.direct = append(b.direct, direct...)
return b
}
// Transitive adds transitive contents to the DepSet being built by a DepSetBuilder. Newly added
// transitive contents are to the right of any existing transitive contents. The argument can
// be any slice of type that has depSet embedded in it.
func (b *depSetBuilder) Transitive(transitive interface{}) *depSetBuilder {
depSets := sliceToDepSets(transitive, b.order)
b.transitive = append(b.transitive, depSets...)
// transitive contents are to the right of any existing transitive contents.
func (b *DepSetBuilder[T]) Transitive(transitive ...*DepSet[T]) *DepSetBuilder[T] {
for _, t := range transitive {
if t.order != b.order {
panic(fmt.Errorf("incompatible order, new DepSet is %s but transitive DepSet is %s",
b.order, t.order))
}
}
b.transitive = append(b.transitive, transitive...)
return b
}
// Returns the depSet being built by this depSetBuilder. The depSetBuilder retains its contents
// Returns the DepSet being built by this DepSetBuilder. The DepSetBuilder retains its contents
// for creating more depSets.
func (b *depSetBuilder) Build() *depSet {
return newDepSet(b.order, b.direct.Interface(), b.transitive)
func (b *DepSetBuilder[T]) Build() *DepSet[T] {
return NewDepSet(b.order, b.direct, b.transitive)
}
// walk calls the visit method in depth-first order on a DepSet, preordered if d.preorder is set,
// otherwise postordered.
func (d *depSet) walk(visit func(interface{})) {
visited := make(map[*depSet]bool)
func (d *DepSet[T]) walk(visit func([]T)) {
visited := make(map[*DepSet[T]]bool)
var dfs func(d *depSet)
dfs = func(d *depSet) {
var dfs func(d *DepSet[T])
dfs = func(d *DepSet[T]) {
visited[d] = true
if d.preorder {
visit(d.direct)
@@ -197,155 +168,33 @@ func (d *depSet) walk(visit func(interface{})) {
dfs(d)
}
// ToList returns the depSet flattened to a list. The order in the list is based on the order
// of the depSet. POSTORDER and PREORDER orders return a postordered or preordered left to right
// ToList returns the DepSet flattened to a list. The order in the list is based on the order
// of the DepSet. POSTORDER and PREORDER orders return a postordered or preordered left to right
// flattened list. TOPOLOGICAL returns a list that guarantees that elements of children are listed
// after all of their parents (unless there are duplicate direct elements in the DepSet or any of
// its transitive dependencies, in which case the ordering of the duplicated element is not
// guaranteed).
//
// This method uses a reflection-based implementation to find the unique elements in slice, which
// is around 3x slower than a concrete implementation. Type-safe wrappers around depSet can
// provide their own implementation of ToList that calls depSet.toList with a method that
// uses a concrete implementation.
func (d *depSet) ToList() interface{} {
return d.toList(firstUnique)
func (d *DepSet[T]) ToList() []T {
return d.toList(firstUnique[T])
}
// toList returns the depSet flattened to a list. The order in the list is based on the order
// of the depSet. POSTORDER and PREORDER orders return a postordered or preordered left to right
// toList returns the DepSet flattened to a list. The order in the list is based on the order
// of the DepSet. POSTORDER and PREORDER orders return a postordered or preordered left to right
// flattened list. TOPOLOGICAL returns a list that guarantees that elements of children are listed
// after all of their parents (unless there are duplicate direct elements in the DepSet or any of
// its transitive dependencies, in which case the ordering of the duplicated element is not
// guaranteed). The firstUniqueFunc is used to remove duplicates from the list.
func (d *depSet) toList(firstUniqueFunc func(interface{}) interface{}) interface{} {
func (d *DepSet[T]) toList(firstUniqueFunc func([]T) []T) []T {
if d == nil {
return nil
}
slice := reflect.Zero(reflect.TypeOf(d.direct))
d.walk(func(paths interface{}) {
slice = reflect.AppendSlice(slice, reflect.ValueOf(paths))
var list []T
d.walk(func(paths []T) {
list = append(list, paths...)
})
list := slice.Interface()
list = firstUniqueFunc(list)
if d.reverse {
reverseSliceInPlace(list)
}
return list
}
// firstUnique returns all unique elements of a slice, keeping the first copy of each. It
// modifies the slice contents in place, and returns a subslice of the original slice. The
// argument must be a slice, but is not type-safe due to the lack of reflection in Go.
//
// Performance of the reflection-based firstUnique is up to 3x slower than a concrete type
// version such as FirstUniqueStrings.
func firstUnique(slice interface{}) interface{} {
// 4 was chosen based on Benchmark_firstUnique results.
if reflect.ValueOf(slice).Len() > 4 {
return firstUniqueMap(slice)
}
return firstUniqueList(slice)
}
// firstUniqueList is an implementation of firstUnique using an O(N^2) list comparison to look for
// duplicates.
func firstUniqueList(in interface{}) interface{} {
writeIndex := 0
slice := reflect.ValueOf(in)
length := slice.Len()
outer:
for readIndex := 0; readIndex < length; readIndex++ {
readValue := slice.Index(readIndex)
for compareIndex := 0; compareIndex < writeIndex; compareIndex++ {
compareValue := slice.Index(compareIndex)
// These two Interface() calls seem to cause an allocation and significantly
// slow down this list-based implementation. The map implementation below doesn't
// have this issue because reflect.Value.MapIndex takes a Value and appears to be
// able to do the map lookup without an allocation.
if readValue.Interface() == compareValue.Interface() {
// The value at readIndex already exists somewhere in the output region
// of the slice before writeIndex, skip it.
continue outer
}
}
if readIndex != writeIndex {
writeValue := slice.Index(writeIndex)
writeValue.Set(readValue)
}
writeIndex++
}
return slice.Slice(0, writeIndex).Interface()
}
var trueValue = reflect.ValueOf(true)
// firstUniqueList is an implementation of firstUnique using an O(N) hash set lookup to look for
// duplicates.
func firstUniqueMap(in interface{}) interface{} {
writeIndex := 0
slice := reflect.ValueOf(in)
length := slice.Len()
seen := reflect.MakeMapWithSize(reflect.MapOf(slice.Type().Elem(), trueValue.Type()), slice.Len())
for readIndex := 0; readIndex < length; readIndex++ {
readValue := slice.Index(readIndex)
if seen.MapIndex(readValue).IsValid() {
continue
}
seen.SetMapIndex(readValue, trueValue)
if readIndex != writeIndex {
writeValue := slice.Index(writeIndex)
writeValue.Set(readValue)
}
writeIndex++
}
return slice.Slice(0, writeIndex).Interface()
}
// reverseSliceInPlace reverses the elements of a slice in place. The argument must be a slice, but
// is not type-safe due to the lack of reflection in Go.
func reverseSliceInPlace(in interface{}) {
swapper := reflect.Swapper(in)
slice := reflect.ValueOf(in)
length := slice.Len()
for i, j := 0, length-1; i < j; i, j = i+1, j-1 {
swapper(i, j)
}
}
// reverseSlice returns a copy of a slice in reverse order. The argument must be a slice, but is
// not type-safe due to the lack of reflection in Go.
func reverseSlice(in interface{}) interface{} {
slice := reflect.ValueOf(in)
if !slice.IsValid() || slice.IsNil() {
return in
}
if slice.Kind() != reflect.Slice {
panic(fmt.Errorf("%t is not a slice", in))
}
length := slice.Len()
if length == 0 {
return in
}
out := reflect.MakeSlice(slice.Type(), length, length)
for i := 0; i < length; i++ {
out.Index(i).Set(slice.Index(length - 1 - i))
}
return out.Interface()
}
// copySlice returns a copy of a slice. The argument must be a slice, but is not type-safe due to
// the lack of reflection in Go.
func copySlice(in interface{}) interface{} {
slice := reflect.ValueOf(in)
if !slice.IsValid() || slice.IsNil() {
return in
}
length := slice.Len()
if length == 0 {
return in
}
out := reflect.MakeSlice(slice.Type(), length, length)
reflect.Copy(out, slice)
return out.Interface()
}